Zentail is a web based application, which means you access it exclusively from one of a number of web browsers, and that problems that seem to appear in Zentail can often be resolved by resetting your browser's cache and cookies. This kind of problem may present as a blank screen, a solid grey screen, being stuck in a loop at login, or other odd behavior.
Note: Generally, it is only necessary to clear the Cache and Cookies, not other saved browsing information like field values and logins.
The steps for resetting a browser vary depending on which browser you are using, instructions for each can be found below:
Once you have cleared this information, close and launch your browser once again, then attempt to navigate back to app.zentail.com